Congestive heart failure (CHF) means the heart does not pump out sufficient blood to meet the body's demands. CHF can result from either a reduced ability of the heart muscle to contract (systolic failure) or from a mechanical problem that limits the ability of the heart's chambers to fill with blood (diastolic failure). When weakened, the heart is unable to keep up with the demands placed upon it and the left ventricle (LV) gets backed up or congested—hence the name of the disorder. CHF is a progressive disease. Failure of the left side of the heart (left-heart failure/left-sided failure/left-ventricle failure) is the most common form of the disease.
CHF affects people of all ages including children, but it occurs most frequently in those over age 60, and is the leading cause of hospitalization and death in that age group. Current treatments of CHF include lifestyle changes, medications, and surgery to bypass blocked blood vessels, replace regurgitant or stenotic valves, install stents to open narrowed coronary vessels, install pump assist devices or transplantation of the heart.
Normal cardiac contraction is a finely tuned orchestrated activity dependent on muscle function, ventricular geometry and loading conditions termed preload and afterload. When CHF due to LV systolic failure occurs it is typically associated with changes in the geometry of the ventricles, often called remodeling. The LV becomes dilated and the interventricular septum is deflected into the right ventricle (RV), resulting in decreased LV output/pumping efficiency. Compare FIG. 1A with FIG. 1B. The efficient systolic function of the LV is dependent not only on the strength of the myocardium but also on the LV geometry, the position and shape of the interventricular septum and the geometry and function of the RV. Interventricular dependence has been documented in experimental studies which have evaluated both normal and pathological preparations in animals LV systolic function can be directly influenced by interventions affecting the RV and the position of the interventricular septum.
Surgical pulmonary artery banding (PAB) is a technique that was described more than 60 years ago and is still in use today for children and infants with congenital heart defects, such as overflow of blood to the lungs and volume overload of the LV. PAB is typically performed through a thoracotomy and involves wrapping a band around the exterior of the main pulmonary artery (MPA) and fixing the band in place, often with the use of sutures. Once applied, the band is tightened, narrowing the diameter of the MPA, increasing resistance to flow, reducing blood flow to the lungs, and reducing downstream pulmonary artery (PA) pressure.
Surgical PAB procedures involve the risks present with all surgical procedures. In addition, use of PAB has a number of particular disadvantages and drawbacks. Primary among these drawbacks is the inability of the surgeon performing the procedure to accurately assess, from the hemodynamic standpoint, the optimal final diameter to which the PA should be adjusted. Often, the surgeon must rely upon his or her experience in adjusting the band to achieve acceptable forward flow while decreasing the blood flow sufficiently to protect the pulmonary vasculature.
It is also not uncommon for the band to migrate towards one of the main pulmonary branches (usually the left), resulting in stenosis of the other main pulmonary branch (usually the right). There have also been reports of hardening of the vessels around the band due to buildup of calcium deposits and scarring of the PA wall beneath the band, which can also inhibit blood flow. Flow resistance due to PAB may change over time, and additional surgeries to adjust band tightness occur in up to one third of patients. The band is typically removed in a subsequent operation, for example, when a congenital malformation is corrected in the child or infant.
In addition to the classical use of PAB for treatment of congenital defects in infants and children, there has been a recent report of use of surgical PAB for left ventricle dilated cardiomyopathy (LVDCM) in infants and young children. This method includes increasing the pressure load on the right ventricle by placing a band around the pulmonary artery. The increased pressure in the right ventricle caused a leftward shift of the interventricular septum and improvement of left ventricle function. It was found that the optimal degree of constriction was achieved when the RV pressure was approximately 60% to 70% of the systemic level and so that the interventricular septum slightly moved to a midline position. The success of these procedures in infants and children has been reported to be possibly due to the potential for myocyte recovery and repopulation being significantly greater for infants and young children than for adults. However, it is the position of the inventors that the geometric improvements to the failing heart due to PAB may be responsible, at least partially, for the observed improvements in LV function, and therefore PAB for adult left ventricle heart failure may demonstrate similar improvement in LV function.
It would be desirable to provide a relatively simple PAB device which could be implanted in a minimally-invasive fashion, and which would allow for later adjustment of blood flow through a vessel. Gradual reduction in the diameter of the MPA may be desirable, but is not currently feasible with the surgical PAB approaches described above. In addition, it would be desirable to use PAB for treatment of the mature adult population suffering from left ventricle (LV) failure.
Attempts have been made to create adjustable or less invasive solutions to PAB devices. The FloWatch®-PAB device (Leman Medical Technologies SA) was designed to be surgically implanted around the exterior of the MPA in infants and uses a remote control system in order to make repeated adjustments of the level of constriction of the implanted device without additional surgical interventions.
The MPA is not a favorable location for positioning an implant due to its large diameter (˜30 mm) and short length (˜50 mm). The full length of the MPA is not usable for an implant due to the proximity to the pulmonary valve on one end, and the bifurcation to the pulmonary branches on the other. It is estimated that the usable length of the MPA for the implant is approximately 30 mm. Implantation of a short, wide device into the MPA is very difficult, and there is significant danger that the device will rotate or otherwise not be placed concentric with the MPA, in which case near complete blockage of the MPA could occur. In addition, the device may erroneously be placed either too close to the pulmonary valve or the bifurcation.
The apparatuses of this invention include an anchor frame that anchors the apparatus within a PA branch vessel, which then assists with the accurate positioning of a device frame that may include a medical device within the MAP. Because an apparatus of this invention is deliverable by transcatheter procedure, high risk surgery is avoided. Apparatuses of this invention may be used for treatment of CHF in adults, including LV failure. The apparatuses of this invention may remain in place for an extended time period and may adjustably control the constriction of the MPA for the duration of a therapeutic treatment.